Conventionally, electrophotographic image forming apparatuses such as a copying machine, a printer and facsimile have been known. In these electrophotographic image forming apparatuses, an electrostatic image latent image in accordance with an image is formed on a surface of a photoreceptor drum (toner image bearing member), the electrostatic latent image is developed by a developing device to be a toner image, the toner image is transferred from the photoreceptor drum to a sheet such as paper, and the toner image transferred to the sheet is fixed to the sheet by a fixing device.
In order to comply with full color and high definition, a recent image forming apparatus employs a two component developer (hereinafter simply referred to as a developer) excellent in charging stability of a toner. The developer consists of a toner and a carrier, and is stirred in a developing device. The stirring causes friction between the toner and the carrier. The friction causes the toner to be properly charged.
The toner charged in the developing device, which toner is used for developing the electrostatic latent image, is supplied to a developer bearing member, for example, a surface of a developing roller. The toner supplied to the developer bearing member is carried by electrostatic attraction to the electrostatic latent image formed on the photoreceptor drum. In this manner, the toner image in accordance with the electrostatic latent image is formed on the photoreceptor drum.
Downsizing and speeding up are required for the image forming apparatus. In order to attain speeding up, it is necessary to immediately and sufficiently charge the developer and immediately carry the developer.
For example, Patent Literature 1 discloses a circulatory developing device for solving the above problem. The circulatory developing device is provided with two developer carrying paths through which the developer is circularly carried and two auger screws that carry the developer through the developer carrying paths while stirring the developer, so that a supplied toner is immediately dispersed in the developer and an appropriate quantity of charging is applied to the toner.
Further, Patent Literature 2 discloses another circulatory developing device for solving the above problem. The another circulatory developing device is provided with two developing carrying paths through which the developer is circularly carried and two auger screws that carry the developer through the developer carrying paths while stirring the developer. Further, a magnet that forms a magnetic brush is provided in the developer carrying path below a toner supply opening. The magnet prevents an insufficiently charged toner (low charged toner) from being supplied to the developer bearing member.